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<FONT color="green">001</FONT>    // Copyright 2002-2007 Waterken Inc. under the terms of the MIT X license<a name="line.1"></a>
<FONT color="green">002</FONT>    // found at http://www.opensource.org/licenses/mit-license.html<a name="line.2"></a>
<FONT color="green">003</FONT>    package org.ref_send.promise;<a name="line.3"></a>
<FONT color="green">004</FONT>    <a name="line.4"></a>
<FONT color="green">005</FONT>    /**<a name="line.5"></a>
<FONT color="green">006</FONT>     * A promise for a referent.<a name="line.6"></a>
<FONT color="green">007</FONT>     * &lt;p&gt;<a name="line.7"></a>
<FONT color="green">008</FONT>     * If you conceptualize a reference as being like an arrow, where an invocation<a name="line.8"></a>
<FONT color="green">009</FONT>     * is started at the tail end of the arrow and delivered to the object pointed<a name="line.9"></a>
<FONT color="green">010</FONT>     * to by the head end of the arrow, then a promise is like the tail end of an<a name="line.10"></a>
<FONT color="green">011</FONT>     * arrow which doesn't yet point to anything. The object referred to by a<a name="line.11"></a>
<FONT color="green">012</FONT>     * promise can be determined later. Using a promise, an algorithm can refer to<a name="line.12"></a>
<FONT color="green">013</FONT>     * an object which will be the result of future computation.<a name="line.13"></a>
<FONT color="green">014</FONT>     * &lt;/p&gt;<a name="line.14"></a>
<FONT color="green">015</FONT>     * &lt;pre&gt;<a name="line.15"></a>
<FONT color="green">016</FONT>     *                       reference<a name="line.16"></a>
<FONT color="green">017</FONT>     *                       |<a name="line.17"></a>
<FONT color="green">018</FONT>     *            referrer ----&amp;gt; referent<a name="line.18"></a>
<FONT color="green">019</FONT>     *                     |<a name="line.19"></a>
<FONT color="green">020</FONT>     *                     promise end of the reference<a name="line.20"></a>
<FONT color="green">021</FONT>     * &lt;/pre&gt;<a name="line.21"></a>
<FONT color="green">022</FONT>     * &lt;p&gt;<a name="line.22"></a>
<FONT color="green">023</FONT>     * There are three states for a promise: &lt;em&gt;fulfilled&lt;/em&gt;,<a name="line.23"></a>
<FONT color="green">024</FONT>     * &lt;em&gt;rejected&lt;/em&gt; and &lt;em&gt;unresolved&lt;/em&gt;. A &lt;em&gt;fulfilled&lt;/em&gt;<a name="line.24"></a>
<FONT color="green">025</FONT>     * promise is successfully bound to a referent, which can be either local or<a name="line.25"></a>
<FONT color="green">026</FONT>     * remote. A &lt;em&gt;rejected&lt;/em&gt; promise failed to acquire a referent, and<a name="line.26"></a>
<FONT color="green">027</FONT>     * carries an {@link Exception} specifying the reason for the failure. An<a name="line.27"></a>
<FONT color="green">028</FONT>     * &lt;em&gt;unresolved&lt;/em&gt; promise is in neither the success nor failure state. A<a name="line.28"></a>
<FONT color="green">029</FONT>     * promise is &lt;em&gt;resolved&lt;/em&gt; if it is in either the success or failure<a name="line.29"></a>
<FONT color="green">030</FONT>     * state.<a name="line.30"></a>
<FONT color="green">031</FONT>     * &lt;/p&gt;<a name="line.31"></a>
<FONT color="green">032</FONT>     * @param &lt;T&gt; referent type<a name="line.32"></a>
<FONT color="green">033</FONT>     */<a name="line.33"></a>
<FONT color="green">034</FONT>    public interface<a name="line.34"></a>
<FONT color="green">035</FONT>    Promise&lt;T&gt; {<a name="line.35"></a>
<FONT color="green">036</FONT>        <a name="line.36"></a>
<FONT color="green">037</FONT>        /**<a name="line.37"></a>
<FONT color="green">038</FONT>         * Gets the current referent.<a name="line.38"></a>
<FONT color="green">039</FONT>         * &lt;p&gt;<a name="line.39"></a>
<FONT color="green">040</FONT>         * For example:<a name="line.40"></a>
<FONT color="green">041</FONT>         * &lt;/p&gt;<a name="line.41"></a>
<FONT color="green">042</FONT>         * &lt;pre&gt;<a name="line.42"></a>
<FONT color="green">043</FONT>         * final Promise&amp;lt;Foo&amp;gt; foo = &amp;hellip;<a name="line.43"></a>
<FONT color="green">044</FONT>         * try {<a name="line.44"></a>
<FONT color="green">045</FONT>         *     foo.call().bar();<a name="line.45"></a>
<FONT color="green">046</FONT>         * } catch (final Exception reason) {<a name="line.46"></a>
<FONT color="green">047</FONT>         *     // Either there is no referent, or the bar() invocation failed.<a name="line.47"></a>
<FONT color="green">048</FONT>         *     throw reason;<a name="line.48"></a>
<FONT color="green">049</FONT>         * }<a name="line.49"></a>
<FONT color="green">050</FONT>         * &lt;/pre&gt;<a name="line.50"></a>
<FONT color="green">051</FONT>         * @throws Exception    reason the referent is not known<a name="line.51"></a>
<FONT color="green">052</FONT>         */<a name="line.52"></a>
<FONT color="green">053</FONT>        T call() throws Exception;<a name="line.53"></a>
<FONT color="green">054</FONT>    }<a name="line.54"></a>




























































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